JPH0637987A - Original detector - Google Patents

Abstract

PURPOSE:To detect an original by the use of each difference between the read picture signal and a silver pressure plate on the color space and on the spatial frequency. CONSTITUTION:The characteristic of hue information of an original pressure plate and spatial frequency information is held in advance and the color information is extracted from the read picture signal. An original discriminating device 113 compares the read hue information with the held hue information to obtain a 1st comparison result, and the spatial frequency information is extracted from the read picture signal. An original discriminating device 119 compares the extracted spatial frequency information and the held spatial frequency information to obtain a 2nd comparison result. A gate circuit 120 discriminates whether the read picture signal is the picture signal of the original pressure plate or the picture signal of a sheet-shaped original based on the 1st and 2nd comparison results.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document detecting device, for example, a document detecting device for detecting a document by a device such as an image reading device.

[0002]

2. Description of the Related Art Current copying machines, such as Canon N
P9130, PIXEL-Dio, PIXEL-EPO
Etc., the original detection is performed using the silver pressure plate and the luminance signal of the original. That is, when the silver pressure plate is read by the CCD, the brightness level is very low, and when the brightness level of all the pixels in a certain small area exceeds a certain threshold value, it is detected as a document. Is.

[0003]

However, in a dark background such as a silver halide photograph, the brightness is about the same as or lower than that of the silver pressure plate, and therefore the pressure plate and the original area cannot be correctly discriminated.
Sometimes the original could not be detected properly. The present invention has been made in view of the above-mentioned drawbacks of the conventional example, and an object of the present invention is to use an original by using each difference in the color space and the spatial frequency between the read image signal and the silver pressure plate. The present invention is to provide a document detection device capable of detecting a document.

[0004]

[Means for Solving the Problems]
In order to achieve the object, a document detecting device according to the present invention is a document detecting device for optically reading a sheet-shaped document held by a document pressure plate to obtain an image signal. Holding means for holding each feature in advance, first extracting means for extracting tint information from the read image signal, tint information extracted by the first extracting means, and the holding means First comparison means for obtaining a first comparison result by comparing the color information with the tint information, second extraction means for extracting spatial frequency information from the read image signal, and the first extraction means. Based on the first and second comparison results, and second comparison means for comparing the spatial frequency information extracted by the above with the spatial frequency information held by the holding means to obtain a second comparison result. , Said reading Whether the image signal is that an image signal of the document pressing plate, and a determination means for determining the or an image signal of the sheet original.

[0005]

According to this structure, the holding means holds each characteristic of the tint information and the spatial frequency information of the original pressure plate in advance, and the first extracting means extracts the tint information from the read image signal. The first comparing means compares the tint information extracted by the first extracting means with the tint information held by the holding means to obtain a first comparison result, and the second extracting means Extract spatial frequency information from the read image signal,
The second comparing means compares the spatial frequency information extracted by the first extracting means with the spatial frequency information held by the holding means to obtain a second comparison result, and the judging means is Based on the first and second comparison results, it is determined whether the read image signal is the image signal of the original pressure plate or the image signal of the sheet original.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A full-color copying machine will be described in detail below as a preferred embodiment. The present invention is not limited to this embodiment. FIG. 4 shows a conceptual diagram of the apparatus in one embodiment of the present invention. Reference numeral 401 denotes a document table glass, and the document is placed between the document pressure plate 438. Manuscript 40
2 is illuminated by an illumination 403 and mirrors 404, 40
After passing through 5,406, an image is formed on the CCD 408 by the optical system 407. Further, the mirror 4 is driven by the motor 409.
04, the mirror unit 410 including the illumination 403 has a velocity V
Second driven mechanically by and including mirrors 405, 406
The mirror unit 411 is driven at a speed of 1/2 V to scan the entire surface of the original 402.

Reference numeral 437 denotes a document detection unit, which determines whether the signal read by the CCD is a document, and if it is a document, sends image information to the image processing unit. An image processing unit 412 is a unit that processes image information as an electric signal and outputs it as a print signal. Reference numerals 413, 414, 415, and 416 denote semiconductor lasers, which are driven by the print signals output from the image processing unit 412, and the laser light emitted by each semiconductor laser is a polygon mirror 41.
7, 418, 419, 420 by the photosensitive drum 42
A latent image is formed on 5, 426, 427 and 428. 42
1,422,423,424 are black (B
k), yellow (Y), cyan (C), magenta (M)
Is a developing device for developing a latent image with the toner of
The developed toner of each color is transferred to the paper, and full-color printout is performed.

The paper fed from any of the paper cassettes 429, 430, 431 and the manual feed tray 432 is adsorbed on the transfer belt 434 via the registration roller 433 and conveyed. The photosensitive drums 428, 427, 426, 42 are previously synchronized with the timing of paper feeding.
Toners 5 of the respective colors have been developed, and the toners are transferred onto the paper as the paper is conveyed.

The paper on which the toner of each color is transferred is separated /
The toner is conveyed, the toner is fixed on the paper by the fixing device 435, and the paper is discharged to the paper discharge tray 436. FIG. 1 shows the flow of signals in the document detector 437. In the figure, 1
Reference numerals 01, 102, and 103 are red (R), green (G), and blue (B) CCD sensors, respectively, which are respectively amplified by analog amplifiers 104, 105, 106, and A / D converters 107, 108, 109. , Are respectively output as digital signals. 110,111
Each of them is a delay memory, and corrects a spatial shift between the three CCD sensors 101, 102, 103.

A spatial distance calculator 112 calculates the distance between a point on the RGB color space indicated by the pixel and an RGB signal of the pixel and a predetermined point (described later). Reference numeral 113 denotes a document determination device, which determines whether or not the pixel is on the document by comparing a value calculated by the spatial distance calculator 112 with a predetermined value (described later).
Reference numeral 118 denotes a spatial frequency filter, which outputs a value obtained by applying a predetermined filter to the pixel and its neighboring pixels. 1
Reference numeral 19 is an original document determiner, which determines whether or not the pixel is on the original document by comparing a value calculated by the spatial frequency filter 118 with a predetermined value.

Reference numeral 120 is a gate circuit, and 113, 11
9 outputs the logical product of both document determiners. 114 is a memory, which stores the determination result. Reference numerals 115, 116 and 117 are gate circuits. FIG. 2 shows a block diagram of the spatial distance calculator 112. A given point (r,
The value L ² of the square of the spatial distance between g, b) and the pixel (R, G, B) is given by equation (1). That is, ^{L 2 = (R-r)} 2 + (G-g) 2 + (B-b) 2 ... (1).

In FIG. 2, 201, 202, and 203 are registers, and r is 201, g is 202, and 2 in advance.
B is set to 03. 204,20
Reference numerals 5 and 206 denote subtractors, which are R-r, G-g, and
The value Bb is output. 207, 208, and 209 are multipliers, but as shown in FIG. 2, the squared values of the respective inputs, that is, (R-r) ² , (G-g) ² , (B
-B) Output the value ² .

Reference numeral 210 denotes an adder, whose output is consequently (R-r) ² + (G-g) ² + (B on the right side of the above equation (1).
-B) The value becomes ² . Reference numeral 211 denotes a delay memory, which corrects a deviation from the determination result due to the output of the spatial frequency filter. FIG. 3 shows a block diagram of the document determination unit 113. When the pixel satisfies the following expression (2), the pixel is on the original. That is, L ² > l ² (2) 301 is a register, which is a value on the right side of the equation (2), that is, a value obtained by squaring a certain predetermined distance l (small el) from the point (r, g, b). Is preset.

Reference numeral 302 denotes a comparator, which determines the authenticity of the above equation (2) as shown in FIG. The principle of document determination based on tint information will be described with reference to FIG. The values (r, g, b) given in advance are vectors that represent the pressure plate in the RGB color space. Further, the value 1 given in advance indicates the variation of the read signal of the pressure plate. That is, when the read signal is within the sphere with the center (r, g, b) radius l (hatched portion in FIG. 5), the signal becomes the read signal of the pressure plate.

Now, the read signal vector (R, G, B)
When the distance L between the vector and the vector (r, g, b) is larger than 1, the signal is the original reading signal. Also, L
When is smaller than 1, the signal is a reading signal of the pressure plate. FIG. 6 shows a block diagram of the spatial frequency filter 118. In the figure, 601, 602, 603, 604
Reference numerals 605, 606, and 607 denote flip-flop circuits, which give a delay of 1 pixel each. 608 is a multiplier, 60
Reference numeral 9 is an adder, and reference numeral 610 is an absolute value input circuit for giving an input absolute value.

As described above, the output at the point b is the filter shown in FIG. 8 in the vicinity of the pixel of interest. 6
Reference numeral 11 is a low-pass filter circuit. Reference numeral 612 is a circuit for converting RGB signals into black and white signals. FIG. 7 shows the document determination device 11
9 shows a block diagram of 9.

In the figure, 701 is a register,
A predetermined value, that is, a threshold value for determining whether the document is a document is set in advance. Reference numeral 702 is a comparator, which is a register 7
Whether or not the document is a document is determined by comparing the value set to 01 and the input value. The principle of document detection based on spatial frequency information will be described with reference to FIGS. 9, 10, 11, 12, 13, 14, and 15.

The original pressure plate has a peculiar striped pattern, and by extracting it as a feature, it is judged whether the read signal is the pressure plate or the original. Hereinafter, an example of the case of FIG. 9 will be described. FIG. 9 shows an image read by the image reading device. The original and the pressure plate around it are read and sent as a read signal to the original detector.

FIG. 10, FIG. 11 and FIG. 12 show the read signal in line A of FIG. The vertical axis represents the brightness and the horizontal axis represents the position on the document. At point a in FIG. 6, the signal as shown in FIG. 10 is read. When this signal passes through the spatial frequency filter and reaches point b in FIG. 7, it becomes a signal as shown in FIG. It can be seen that the read signal of the original platen is emphasized by the spatial frequency filter. In some cases, a region having the same component as the spatial frequency component of the original platen may exist in the original document, and the signal is passed through a low-pass filter to remove it as noise. Then,
At point c in FIG. 6, the signal is as shown in FIG. If a value corresponding to T in FIG. 12 is set in the register 702 in FIG. 7 in advance, a signal larger than T indicates a pressure plate, and a signal below T indicates a document, respectively.
The original can be detected.

13 and 14 show frequency spectra of the pressure plate and the original, respectively. 15 shows the frequency characteristic of the spatial frequency filter shown in FIG. When a filter having such a characteristic is applied to the read image of the pressure plate, a frequency component shown in the shaded area of FIG. You can see that it is emphasized.

As described above, according to this embodiment, the original is detected by using each difference in the color space and the spatial frequency between the read image signal and the silver pressure plate, so that the luminance signal can be detected. It is possible to improve the accuracy of document detection, as compared with the conventional method using the.

[0022]

[Other Embodiments] Next, other embodiments will be described. An example
For example, the memory 114 shown in FIG.
May be performed. Also, the spatial distance
The calculation is not limited to the RGB color space.
If L ^* a^* b^* It may be on another color space such as a color space.

Further, in the spatial distance calculator shown in FIG. 2, the multipliers 207, 208 and 209 can be replaced with a look-up table composed of a ROM. This example is shown in FIG. 1601, 1602, 1
603 are (R-r) ² , (G-g) ² , and (B-, respectively).
b) It is a lookup table for performing the calculation of ² . Other configurations are the same as those in FIG. 2, and thus description thereof will be omitted.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0025]

As described above, according to the present invention, the original is detected by using each difference in the color space and the spatial frequency between the read image signal and the silver pressure plate to detect the luminance signal. It is possible to improve the accuracy of document detection as compared with the conventional method that uses the case.

[Brief description of drawings]

FIG. 1 is a diagram showing a signal flow of a document detection unit.

FIG. 2 is a block diagram of a spatial distance calculator.

FIG. 3 is a block diagram of a document determination device.

FIG. 4 is an external view of the device.

FIG. 5 is a diagram illustrating document detection based on tint information.

FIG. 6 is a block diagram of a spatial frequency filter.

FIG. 7 is a block diagram of a document determination device.

FIG. 8 is a diagram showing a shape of a spatial frequency filter.

FIG. 9 is a diagram illustrating document detection based on spatial frequency information.

FIG. 10 is a diagram illustrating document detection based on spatial frequency information.

FIG. 11 is a diagram illustrating document detection based on spatial frequency information.

FIG. 12 is a diagram illustrating document detection based on spatial frequency information.

FIG. 13 is a diagram showing frequency spectra of a pressure plate and a document.

FIG. 14 is a diagram showing frequency spectra of a pressure plate and a document.

15 is a diagram showing frequency characteristics of the spatial frequency filter shown in FIG.

FIG. 16 is a diagram illustrating another example.

[Explanation of symbols]

101, 102, 103 CCD sensor 104, 105, 106 Analog amplifier 107, 108, 109 A / D converter 110, 111 Delay memory 112 Spatial distance calculator 113, 119 Original judgment device 114 Memory 115, 116, 117 Gate circuit 118 Spatial frequency filter 119 Original determination device 120 Gate circuit 201, 202, 203 Register 204, 205, 206 Subtractor 207, 208, 209 Multiplier 210 Adder 211 Delay memory 401 Original platen glass 402 Original 403 Illumination 404, 405, 406 Mirror 407 Optical system 408 CCD 409 Motor 409 410 Mirror unit 411 Second mirror unit 412 Image processing unit 413, 414, 415, 416 Semiconductor laser 417, 418, 419, 4 0 polygon mirror 421, 422, 423, 424 developing device 425, 426, 427, 428 photosensitive drum 429, 430, 431 paper cassette 432 manual feed tray 433 registration roller 434 transfer belt 437 document detector 438 document pressure plate 601, 602, 603, 604 Flip-flop circuit 605, 606, 607 Flip-flop circuit 608 Multiplier 609 Adder 610 Absolute value input circuit 1601, 1602, 1603 Look-up table

Claims (2)

[Claims] 1. A document detection device for optically reading a sheet-shaped document held by a document pressure plate to obtain an image signal, and holding means for holding respective features of tint information and spatial frequency information of the document pressure plate in advance. Comparing the tint information extracted by the first extracting unit with the tint information held by the holding unit, and extracting the tint information from the read image signal, First comparing means for obtaining a first comparison result, second extracting means for extracting spatial frequency information from the read image signal, spatial frequency information extracted by the first extracting means, and the holding Second comparison means for comparing the spatial frequency information held by the means to obtain a second comparison result, and the read image signal based on the first and second comparison results. Of platen Whether an image signal,
An original detection device comprising: a determination unit that determines whether the image signal is the image of the sheet original. 2. The image forming device according to claim 1, further comprising an image forming device that forms a visible image when the determination device obtains a determination result that the image signal is an image signal of the sheet original. Document detection device.